Modeling Magnetostrictive Transducers for Structural Health Monitoring: Ultrasonic Guided Wave Generation and Reception.

Gaofeng Sha,Cliff J. Lissenden

doi:10.3390/s21237971

Abstract

Ultrasonic guided waves provide unique capabilities for the structural health monitoring of plate-like structures. They can detect and locate various types of material degradation through the interaction of shear-horizontal (SH) waves and Lamb waves with the material. Magnetostrictive transducers (MSTs) can be used to generate and receive both SH and Lamb waves and yet their characteristics have not been thoroughly studied, certainly not on par with piezoelectric transducers. A series of multiphysics simulations of the MST/plate system is conducted to investigate the characteristics of MSTs that affect guided wave generation and reception. The results are presented in the vein of showing the flexibility that MSTs provide for guided waves in a diverse range of applications. In addition to studying characteristics of the MST components (i.e., the magnetostrictive layer, meander electric coil, and biased magnetic field), single-sided and double-sided MSTs are compared for preferential wave mode generation. The wave mode control principle is based on the activation line for phase velocity dispersion curves, whose slope is the wavelength, which is dictated by the meander coil spacing. A double-sided MST with in-phase signals preferentially excites symmetric SH and Lamb modes, while a double-sided MST with out-of-phase signals preferentially excites antisymmetric SH and Lamb modes. All attempted single-mode actuations with double-sided MSTs were successful, with the SH3 mode actuated at 922 kHz in a 6-mm-thick plate being the highest frequency. Additionally, the results show that increasing the number of turns in the meander coil enhances the sensitivity of the MST as a receiver and substantially reduces the frequency bandwidth.

Highlights

Accepted: 25 November 2021Research and practice in using ultrasonic guided waves for the structural health monitoring (SHM) of plate-like structures has focused more on Lamb waves than shearhorizontal (SH) waves, perhaps because Lamb wave modes are easier to generate using an angle-beam transducer and gel couplant [1]
Magnetostrictive transducers (MSTs) generate SH waves well and can generate some of the Lamb wave modes that are more difficult to excite with angle-beam transducers; for example, the nonleaky S1 mode when the phase velocity is equal to the longitudinal wave speed [8]
The transducer and plate materials used in the finite element modeling as well as the methods used to prescribe the transducer geometry and loading are described

Summary

Introduction

Research and practice in using ultrasonic guided waves for the structural health monitoring (SHM) of plate-like structures has focused more on Lamb waves than shearhorizontal (SH) waves, perhaps because Lamb wave modes are easier to generate using an angle-beam transducer and gel couplant [1]. Lamb waves (having displacement profiles with two components) and their interaction with discontinuity (e.g., cracks and section loss) are more complicated [5] while SH waves (having displacement profiles of just one component) can exhibit simpler mode conversion behavior when interacting with a defect [6] Another advantage of SH waves is that they do not leak into the fluid at the plate surface, while most Lamb wave modes are leaky, which causes significant attenuation when the plate is fluid loaded [7]. Magnetostrictive transducers (MSTs) generate SH waves well and can generate some of the Lamb wave modes that are more difficult to excite with angle-beam transducers; for example, the nonleaky S1 mode when the phase velocity is equal to the longitudinal wave speed [8]

Objectives

Methods

Results